Symmetric Multiprocessing

SMP lets multiple CPUs in a networking device share the same board, memory, I/O and operating system. Nonetheless, each CPU in an SMP system can act independently. While one CPU handles a database lookup, others can update the database and perform other tasks, dramatically increasing the ability of the device to handle today's increasingly complex networking tasks.

SMP costs relatively little. When scaling from one CPU to two, only one processor board is needed. Processing power is doubled without paying for additional support chips and without taking up an additional slot in the chassis.

Despite its benefits, SMP can only scale so far. Bottlenecks can occur when several CPUs on a board share a single memory bus. Rather than put too many CPUs on the same SMP board, designers of high-end network elements can distribute applications across a networked cluster of SMP boards, where each board has its own memory array, I/O and operating system.

This approach has its challenges. For instance, network managers have to add network-specific code to applications so they can "talk" to each other across the networked boards. Also, because drivers and protocols in most operating systems are bound to the kernel, moving any of them from one board to another means you have to create and carefully test a new kernel image for each board.